A cuff is a special fabric at the lower edge of the sleeve or pant leg, approximately where the wrist or ankle is. The term cuffs (usually in plural because it comes in pairs) can also refer to a means of restraint that is attached to the wrists (see handcuffs) or ankles. Other variants exist but play a minor role, such as thumbcuffs or testicle cuffs.
Cuffs for bondage
In BDSM, both hand and ankle cuffs are popular for bondage in various positions. They often come in sets two pairs: though wrist and ankle cuffs are different in diameter. Cuffs can be attached to one another, to items of furniture (e.g. a St. Andrews Cross), or to attachment points at the ceiling, wall, or floor.
Cuffs can either be first attached to the bottom's body and then to the point of restraint, or they can be first (or permanently) attached to somewhere (e.g. an item of BDSM furniture) and then the bottom's wrist or ankle is brought to this attachment point and secured there. Ankle cuffs can also be attached to spreader bars.
Cuffs can be made of steel (like traditional handcuffs or shackles), but bondage cuffs are usually made from a strong yet flexible material such as leather or nylon. Such bondage cuffs are usually closed with buckles, and usually come with a D-ring where a strap, rope, chain etc. can be attached.
The use of handcuffs, even with soft coverings, for bondage can, in some instances, lead to severe and permanent damage of nerves, blood vessels and body extremities.
In modern BDSM, cuffs are often padded on the inside so they are more comfortable (while still secure), and also safer as they won't block blood circulation this way. Still, subjects should never be suspended from normal bondage cuffs - there are special suspension cuffs which are safe for suspension.
Woman in BDSM collar, her wrists in cuffs behind her back (2008).